1. Field of the Invention
The technical field of the present specification relates to a Group III nitride semiconductor light-emitting device and a production method therefor. More specifically, it relates to a Group III nitride semiconductor light-emitting device having a low drive voltage, and a production method therefor.
2. Background Art
For the Group III nitride semiconductor light-emitting device, there is no electrode material having a work function that can achieve complete ohmic contact with a p-type contact layer, e.g., a p-type GaN layer. Therefore, a Schottky Contact is formed between the p-type contact layer and the p-electrode. To reduce the contact resistance, preferably, carriers easily tunnel through the Schottky barrier by the tunnel effect. For example, the Schottky barrier is thinned by doping a p-type dopant to the p-type contact layer at a high concentration. Furthermore, to make the carriers easier to tunnel through the Schottky barrier, there are preferably some crystal defects in the Schottky barrier because the carriers easily tunnel through the Schottky barrier by a hopping conduction via the crystal defects.
Japanese Patent Application Laid-Open (kokai) No. 08-097471 discloses a light-emitting diode 10 comprising a second contact layer 62, and a first contact layer 63 having a Mg concentration higher than that of the second contact layer 62 (refer to paragraph [0011] and FIG. 1). Thus, a light-emitting diode having a low drive voltage was obtained (refer to paragraph [0009]).
To make the carriers easily tunnel through the Schottky barrier by the tunnel effect, the concentration of the p-type dopant, for example, Mg, that is doped to the p-type contact layer is increased. For that purpose, a high-concentration p-type dopant must be incorporated in the semiconductor crystal by increasing the concentration of the p-type dopant gas.
However, right after the supply of the p-type dopant gas was started or when the supply amount of the p-type dopant gas was quickly increased, the dopant concentration of the growing p-type contact layer is lower than a desired dopant concentration. The dopant concentration of the p-type contact layer tends to increase as the thickness increases, that is, the growth time passes. This achieves the desired dopant concentration near the contact surface of the p-type contact layer.
Since the dopant gas or particles generated from the gas adsorbs on the inner wall of the chamber by the memory effect, the gas concentration is considered to be unstable right after the supply of the p-type dopant gas was started or increased in a step function. Therefore, the desired gas concentration is not achieved on the crystal growth surface. Or, a high dopant concentration is not achieved in a thin contact layer due to a characteristic that the p-type dopant is difficult to be incorporated in the Group III nitride semiconductor. To achieve the desired concentration of the p-type dopant (impurity) in the semiconductor, the p-type contact layer must have a thickness larger than the thickness of the Schottky barrier. The electric resistivity is increased due to increase of excessive series resistance component or occurrence of unintentional crystal defect, thereby increasing the drive voltage. Thus, to produce a semiconductor light-emitting device having a low electric resistivity, it is important to provide a p-type contact layer having a small thickness and a high p-type dopant concentration.